You must have a written appraisal from a qualified appraiser that supports the information. However, see the Exceptions below.
Generally, you do not need to attach the appraisals but you should keep them for your records.
1. A qualified vehicle (including a car, boat, or airplane) if your deduction for the vehicle is limited to the gross proceeds from its sale and you obtained a contemporaneous written acknowledgment;
2. Intellectual property (as defined earlier);
3. Publicly traded securities and certain securities considered to be publicly traded (as defined in Which Sections To Complete, earlier); or
4. Inventory or property held primarily for sale to customers in the ordinary course of your trade or business